TS 

837 

.A b 




"ANDREWS" 

Lumber Driers 



BULLETIN 200 



PRINCIPLES 

OF 

Lumber Drying 

AND 

Instructions to 
Operators 



The A. H. Andrews Go. 

CHICAGO 



PRINCIPLES 

OF 

Lumber -Drying 

AND 

Practical Advice 

TO 

Dry Kiln Operators 



Compiled by 

The Drier Department - Engineering Division 

OF 

THE A. H. ANDREWS CO. 

115-117 So. Wabash Avenue 

CHICAGO 
Manufacturers of Efficient Dry Kilns 



E 



A* 



COPYRIGHT 1914 

By THE A. H. ANDREWS CO. 
Chicago, III. 

All rights reserved. 



U 



FEB -9 1314 



©CI.A361911 



PRINCIPLES OF LUMBER DRYING 3 M 



PREFACE. 

(1) The time has passed when Dry Kilns were bought and 
sold like the lumber which they were to dry, with consideration of 
first cost only, regardless of ultimate efficiency and economy, and 
were installed and connected to steam supply and condensation re- 
turn in an indifferent manner. 

(2) The careful and better informed purchaser of Dry Kiln 
equipment of the present day requires a fair amount of COM- 
PETENT ENGINEERING attention to his Dry Kiln problems which 
the up-to-date and wide-awake manufacturer of Dry Kiln equipment 
is only too willing to provide, because he realizes that by this means 
he will be able to insure a proper and satisfactory working of the 
kilns which he designs and supplies. 

(3) The time also has passed, when upon completion, the Dry 
Kiln was turned over to the operator with a few "verbal" instruc- 
tions, very general and vague, which were considered sufficient to 
secure the desired drying results. 

(4) Wise purchasers of Dry Kiln Equipment require correct 
information, more tangible than mere talk, and the wise Manufac- 
turer of Dry Kiln equipment, welcomes and satisfies this desire for 
information, appreciating that an understanding of the principles 
involved in the correct drying of Lumber will enable the Owners and 
Operators of his Dry Kilns to obtain satisfactory results from same. 

(5) THE A. H. ANDREWS CO. continually striving for im- 
provement of their Dry Kiln apparatus and results of its operation, 
have created for the benefit of purchasers and users of the "AN- 
DREWS DRY KILNS" an ENGINEERING SERVICE DEPART- 
MENT, comprising the best talent, information and experience in 
DRYING, in HEAT TRANSMISSION, in AIR MOVEMENT, and 
in all matters pertaining to STEAM from its making to its final 
application. 

(5-a) The object of this Engineering Department is to make 
a careful survey of the requirements of any prospective purchasers 



pi 

B 4 PRINCIPLES OF LUMBER DRYING 

g of Dry Kiln Equipment and to give logical and correct information g 
= and advice. 

S ( 6 ) To treat each and every case as ' ' special ' ' and ' ' individual ' ' 

= and with that care which it requires and deserves and to design 

H each Dry Kiln so that it may perform efficiently and economically the 

g work required from it under the conditions surrounding its opera- 

(7) And finally to properly instruct and advise the users of the g 
g " ANDREWS" Dry Kilns as to their correct, efficient and economic 

U OPERATION not by mere verbal instructions, but by practical, 
II readily understood (and conveniently referred to) printed matter, 
HI carefully compiled, authentic and extended from time to time. 

H Correct Drying Conditions 

(8) The proper drying of lumber is not a very, complicated g 
g matter, but it is based upon principles which may be readily ab- 

j§§ sorbed and understood by anyone who wishes to exercise a little g 

Hj thought, study and trouble to understand the same, and, once their 

§§ meaning has been grasped, the rules and instructions supplied for || 

jjj the proper operation of the several types of kilns will assume a plain 

JH and simple meaning, never again to be forgotten. 

(9) There is probably no other operation in the "Wood Working 
H Industry in which the result depends so absolutely upon faithful 

II fulfillment of a few simple conditions as does the proper drying of g 
g lumber in Kilns. 

(10) To perfectly dry lumber in any Kiln certain conditions 
J of HEAT, HUMIDITY, and CIRCULATION must be provided, 
= which will vary with the species of lumber and its initial moisture 
g content when introduced into the Kiln. 

(11) No matter what the name, type, design or construction 
Hi of the Kiln, the lumber to be dried must be surrounded in all its 

HI parts by these necessary conditions if it is to come out of the Kiln g 
g in a state of greatest perfection, free from defects, and within the gj 
H shortest possible time. 



PRINCIPLES OF LUMBER DRYING 5 

(12) Lumber which has been partially air dried in the open of Jj 
necessity has been exposed to the varying conditions of the weather, [g 
and its drying, though perhaps very slow, has been far from uni- 
form and mostly on the surface. J 

(13) Sun heat and sharp winds have caused a closing of the = 
cells and a hardening of the fibers of the exposed surfaces of the 
lumber to such an extent as to seriously retard the passage of the gj 
moisture from the central inner portion of the wood to its outer sur- 
face, n 

(14) If lumber in this condition of contracted outer cells and 1§ 
hardened fibers is placed into a Dry Kiln and subjected at once, and U 
without further preparation, to a high temperature, then the drying ^ 
outer surface of the wood, shrinking and unable to compress the inner, j| 
still moist cells and fibers will be liable to crack or check, while the || 
inner portions, drying more slowly and unable to contract the adjoin- 
ing outer parts, are apt to rupture or honeycomb in their setting. 

(15) The first principle in the drying of lumber (and particu- g 
larly of Hard "Wood Lumber) therefore to be remembered is: 

"That the temperature of the Lumber must not be 
increased until after the outer fiber and cell structure 
has been properly conditioned to readily permit its har- 
monious contraction and set in drying with the inner 
portion of the wood. ' ' 

(16) This conditioning of the outer layers of the wood can = 
only be accomplished by "RATIONAL STEAMING" of the lumber, 
and in no other way can the partially case hardened surface layers of 

the wood be again made permeable to the internal moisture. 

(17) The moderate steaming will at the end of the steaming j 
period also have somewhat increased the temperature of the lumber 
but not sufficiently for drying, especially if the wood is of consid- 
erable thickness. 

(18) Moreover the warming of the lumber must be gradual and §H 
should be "no faster" than the heat can pass through the lumber §| 
to its innermost core. 

(19) Until the lumber temperature (in the central portion of g 



jjll 

■ 6 PRINCIPLES OF LUMBER DRYING 

HI all boards constituting the pile), has been almost equalized to the 

jg temperature of the surrounding kiln air (prescribed by the species 

= of wood being dried), no moisture whatever must be removed from 

H the outer surface of the wood, and no actual "drying" must take 

jj place. 

(20) The second important principle in the drying of lumber 

!§ (and particularly of Hard Wood Lumber), to be remembered is: 

"That no moisture whatever must be abstracted from 

the wood until the temperature of all parts of the wood 

(clear to its very center) has been almost equalized to the 

temperature of the surrounding kiln air, which latter tem- 

H perature is limited by the nature of the wood to be dried." 

H (21) The moisture of the central portion of the boards can be 

H driven to the surface and removed only if and as the the necessary 

HI heat is supplied, and only as fast as the moisture is enabled to pass 

fU the intervening cells and fibres to the outer surface of the boards. 

(22) Since no movement of the "inner" moisture of the lumber 
j§ can take place without heat, therefore, any attempt to remove moisture 
H from the kiln air before all parts of the wood (and moisture con- 
= tained therein) have been brought to equal temperature, would result 
jH in surface drying (vaporization, like all other processes of nature, 
H following the path of least resistance), and this in turn would induce 
jj ease hardening with all its accompanying troubles. 

(23) After the lumber has been properly steamed, and its 
g surface has become permeable to the passage of its inner moisture, 
jg and the wood as well as its moisture content has been heated through 
HJ and through as near to the temperature of the surrounding kiln air 
HI as it is possible, then actual drying may safely begin, and if the 
Hi drying process is carried on in a logical and correct manner, the 
j| inner moisture will move, slowly but surely from the eenter of the 
HI wood to its surface, there to be vaporized and absorbed by the kiln 
|§ air. 

(24) But the progress of the inner moisture to the surface 
H of the lumber will depend upon the resistance opposing it and 

upon its own inherent force or pressure. This resistance in turn is 



1,7. 



PRINCIPLES OF LUMBER DRYING 7 

proportional to the thickness of the board walls through which this 
moisture must pass, and also is influenced by their structure (accord- ^ 
ing to the species of wood), while the force (or pressure) of the 
vapors and moisture seeking to pass through the surrounding wood 
structure is largely dependent upon their temperature. 

(25) Assuming therefore, that it is within the power of the jj| 
Dry Kiln operator (as in most Dry Kilns it really is, and as in every 
case it should be) to so condition the kiln air as to cause it to absorb §| 
the moisture more or less rapidly, then, if the moisture forced from §| 
the center of the wood is not absorbed by the surrounding air as 
fast as it issues, the drying process will be simply retarded, while on (§ 
the other hand if the air does absorb moisture faster than the same 
can progress from the inner cells of the wood to its surface, then |g 
surface drying and its attendant troubles of case hardening, check- ||f 
ing, honey combing, etc., will surely result. 

(26) Thus the third condition of importance in the drying of | 
Lumber (and particularly of Hard Wood Lumber), to be remem- 
bered is : 

"That the moisture must not be removed from the 
wood (absorbed by the Kiln Air) any faster than this mois- 
ture can pass from the inner structure ef the wood to its 
surface, otherwise surface drying, case hardening and trouble 
will result." 

(26-a) The condition stated in the preceding paragraph be- 
comes especially important after nearly all the free moisture has §§ 
been transmitted from the inside of the wood to its surface and that jj 
point has been reached in the drying period when the fibers themselves 
must give up their moisture content. 

(26-b) It is at this point, when shrinkage begins, that the 
speed of the moisture removal or drying must be properly retarded, 
to enable the wood to gradually adjust itself to the changing con- H 
dition. 

(26-c) Too fast drying is injurious at any time, but becomes 
much more so at this critical point of the drying period. 

(27) A careful consideration of the hereinbefore stated prin- 



jj 8 PRINCIPLES OF LUMBER DRYING 

H ciples will readily disclose the necessity for properly controlled, uni- 

| form and continuous conditions of the TEMPERATURE of the lum- 

jj ber to be dried, and of the TEMPERATURE, HUMIDITY, and 

H MOVEMENT of the AIR surrounding this lumber. All of these 

|§ conditions must be gradually changed as required during the prog- 

g ress of the drying process, but the same must be uniformly main- 

II tained within these gradual variations. 

H Interrupted Drying 

= (28) The same careful consideration will also disclose the 

§| danger to the lumber (particularly Hard Wood Lumber) from "IN- 

g TERRUPTED DRYING," as frequently practiced in plants where 

|H steam is either not at all or indifferently kept up during the night and 

g on Sundays. 

U (29) Unless under such conditions particular attention is paid 

g to the protection of the lumber against the otherwise unavoidable 

g surface drying, indifferent results are bound to follow, because with. 

jl such interruptions the required condition of humidity can be main- 

g tained only with difficulty and by special care. 

(30) Whenever the steam supply to any Dry Kiln is inter- 
g rupted for any appreciable length of time, then not only is temper- 
g ature of the Kiln air reduced, but also its humidity is very much more 
g reduced than the temperature, and quick surface drying may result 
g until the heat stored up in the lumber has been exhausted, unless pre- 
g caution is taken to supply an excess of Moisture by means of direct 
g wet steam. 

(31) After such an interruption, when the steam supply is 
g again restored to the heating coils of the kiln, a sufficient amount of 
g direct steam must again be discharged into the kiln to bring up the 
g humidity to the point prescribed for the temperature and period 
g of the drying process until the heat shall once more cause the moisture 
g to move from the inner parts of the wood and the lumber will supply 
g all moisture required to maintain the necessary humidity of the Kiln 
■ Air. 

(32) If this is not done, or if indifferently done, indifferent 
g drying only can be expected. 



RINCIPLES OF LUMBER DRYING 9 §| 

Air Circulation 

(33) In the preceding paragraphs certain conditions have been |i 
described as very important to good results. To obtain these con- 
ditions it is but necessary to properly control the "TEMPERA- !g 
TURE" and "HUMIDITY" of the Kiln Air. 

(34) There is, however, another and equally as important a con- || 
dition which must be provided to bring about the desired good and g 
quick results. 

(35) A continuous and sufficiently rapid MOVEMENT of the ■ 
properly heated and humidified kiln air over all surfaces of all the H 
lumber in each stack must be provided. 

(36) This "CIRCULATION" of the Kiln Air must bring (j 
heat and humidity to the lumber in the center of the pile and must j=| 
carry away the released moisture in the same measure as it performs § 
this service for the lumber in the more accessible top, side and bot- g 
torn portions of each respective pile. 

(37) The amount of free space therefore, which is left between g 
the boards of the pile will in a large measure influence the much g 
needed circulation of the Kiln Air through the pile. 

(38) The proper PILING and "STICKING" of the lumber g 
consequently becomes of first importance, next to the correct design = 
and proportioning of the kiln and its equipment. 

(39) If sufficient access is not provided for the Kiln Air to pass jj| 
through the entire pile and around each side of each board com- 
posing the respective pile, then since the Kiln Air is the only medium |j 
to convey the heat to the wood and to remove the moisture from the j| 
wood, the drying process will be retarded in the same measure as the 
progress of the air through the pile is retarded by insufficient spacing g 
of the lumber. 

(40) To avoid any possible misunderstanding it is necessary 
to state that by "Circulation" of the Kiln Air is meant that amount 
of movement (or velocity) of the air necessary to accomplish the serv- 
ice required, and no more. Let, therefore, no one be misguided into 



H 10 PRINCIPLES OF LUMBER DRYING 

j§ the belief, that if little is good, more would be better with "any" type 

H of kiln. 

(41) Excessive Air Circulation through a "Ventilated" kiln 

= would prove not only expensive (since the air must be heated), but 

= also disastrous to the lumber itself, unless such circulation could be 

HI made strictly "internal," under perfect humidity control, and with- 

U| out influence upon the fresh air supply and moist air removal. 

HI (42) It is because in most Kilns the Air is "MOVED 

H SLOWLY" and with but little force to accomplish its movement, that 

H the requirement for sufficient air space between the boards of each 

= respective pile becomes so important. 

U Controlling Factors 

= (43) In reviewing what has been hereinbefore set down it will 

H= be noted that four factors are required to effect the proper forced 

HI drying of wood. 

H 1-HEAT. 

jj 2 -HUMIDITY. 

M 3-CIRCULATION. 

J 4-TIME. 

= (44) A proper combination and progressive variation of the 

II first three factors will not only reduce the (fourth) factor of TIME, 

11 but the correctly and progressively varied combination of all four will 

JH materially affect the quality of the finished product. However, all are 

= strictly dependent upon the correct design and construction of the 

HI kiln and upon faithful supervision of its operation. 

■ Heat 

(45) The HEAT is controlled by the regulation of the steam 
H supply. This regulation may be by hand or automatic, but in any 
!§ event, the steam pressure must be constant and the supply continuous 
H if best results are to be obtained. 

(46) Constant pressure of Steam at the Kiln, free from any 
fH variation due to fluctuations in firing of the boilers can be obtained 
§H only if the pressure of the steam is materially and automatically re- 



n 



PRINCIPLES OF LUMBER DRYING II 

duced at point of its passage into the Kiln supply main. A suitable 
automatic pressure reducing valve of good construction will readily 1| 
maintain uniform pressure in this supply main, and therefore, uni- gj 
form kiln temperature and humidity conditions. 

(47) If exhaust steam from engines or pumps or other sources H 
is available it should by all means be utilized, because it represents g 
a net saving. In such case the heating surface of the coils will have 

to be a little larger than whCn "live" steam is used. But with the |jj 
use of exhaust steam (at a back pressure of not less than iy 2 pounds) = 
provision must be made for a constantly available supply of "live" = 
steam into the Dry Kiln line through a suitable, well constructed pres- ||| 
sure reducing valve, which shall automatically admit live steam when- 
ever the supply of exhaust steam falls below the requirement of the = 
Kiln Coils. Such an arrangement would also require the installation |g 
of a suitable "back-pressure" valve in the atmospheric exhaust line of 
the engines, in order that the exhaust steam may be maintained at |jl 
the required uniform back pressure of iy 2 pounds. 

(48) But even with all these precautions of continuous steam 
supply at constant pressure it will not be possible to establish and m 
maintain uniform kiln temperature (and consequently humidity) §j 
unless the condensation is removed from the coils promptly and con- }§| 
tinuously as fast as made, and with this condensation any aceumu- = 
lations of air in the coils. 

(49) Thus the performance of the return lines and condensa- 
tion removal apparatus becomes fully as important as that of the j§ 
steam supply. Without the proper function of either good results 
cannot be expected. JH 

Humidity 

(50) The necessary amount of HUMIDITY of the Kiln Air is B 
obtained by means of the injection of steam into the kiln during the 
first stage of the drying process and later from the moisture which 

is being evaporated from the wood. 

(51) The relative amount of humidity of the Kiln Air (or =j 
in other words, the amount of water vapor suspended in the kiln 



m 12 PRINCIPLES OF LUMBER DRYING 

HI air per cubic foot) is controlled in Moist Air Kilns by regulating 

HI the quantity of the air entering into and escaping from the kiln. 

m (52) In Condensing Kilns the humidity is controlled by the 

HI amount of cooling surface and temperature of the condenser coils. 

(53) As hereinbefore stated, it is the humidity of the Kiln Air 

II which controls the rate of evaporation of the moisture from the 
HI wood (assuming that the correct kiln temperature is maintained). 
Hi In Moist Air Kilns the volume of fresh air continuously passing 
p| into the kiln, and the consequent continuous removal from the kiln 
H| of an equal volume of moist air, controls the degree of percentage of 
!§ humidity. In Condensing Kilns the amount of moisture continuously 
HI eliminated by the condenser coils, controls the humidity of the Kiln 
HJ Air. 

= (54) Thus becomes self-evident the importance of careful atten- 

m tion to the adjustment of the fresh air supply and moist air removal 

|H dampers of Moist Air Kilns, and the same attention to the adjust- 

III ment of the water supply passing through the cooling coils of the 
HI Condensing Kilns, all in harmony with the humidity conditions re- 
== quired for the drying of the various species of lumber. 

jj Circulation 

Hj (55) The circulation in a Moist Air Kiln is twofold. The 

Hj heated air rises from the coils, passing through the lumber piles, 

Hj gives up part of its heat in exchange for some moisture, and issuing 

=J through the horizontal spaces between the boards, (considerably 

HJ cooler and therefore heavier) the bulk of the air drops to the bottom 

Hj of the Mln, only to pass over the coils again, while a smaller volume 

=j is permitted to escape through the ventilator stacks, carrying with 

Hj it a certain amount of moisture. 

(56) The volume of air thus continuously removed is just as 

Hj continuously replaced by fresh air taken into the kiln through the 

§j supply ducts and passed to the under side of the coils, there to mix 

|H with the moist kiln air, thus reducing its relative humidity and pre- 

= paring it to take up more moisture from the lumber on its passage 

Hj through the free spaces between the boards of each pile. 



PRINCIPLES OF LUMBER DRYING 13 || 

(57) In a CONDENSING KILN the circulation of the air is 
simpler. The heated air rising from the heater coils is passed through jjj 
the lumber piles and issuing between the boards, charged with the 
moisture which it has absorbed from the lumber, and also slightly 1§ 
cooled, it is " drawn" to the condensing chamber where in passing = 
over the cool surface of the condenser coils it becomes cooled and g 
consequently heavier to such an extent that it drops with considerable 
velocity to the distributing chamber under the heating coils in order 

to pass again over the heater coils and to repeat the cycle. 

(58) The force of the cooled air dropping in the condenser = 
chamber is sufficient to "draw" the moist air issuing from the lum- j|| 
ber piles over the top and into this condenser chamber, and to thus 
maintain an ample circulation within the kiln which otherwise is U 
closed air tight. H 

Time 

respective species may be safely exposed, 
lumber will depend : HI 

1-Upon the "INITIAL" MOISTURE CONTENT of 
the wood. 

2-Upon the desired "FINAL" MOISTURE CON- 
TENT, or point of dryness. 

3-Upon the MAXIMUM TEMPERATURE to which 
the respective species may be safely exposed. 

4-Upon the RESISTANCE of the eeUular and fibre 
structure of the wood to the TRANSMISSION of 
MOISTURE. 

5-Upon the THICKNESS of the lumber. 

6-Upon the CAREFUL regulation of TEMPERA- 
TURE and HUMIDITY. 

7-Upon the CORRECT CONSTRUCTION of the kiln 
with regard to proper CIRCULATION and MOIS- 
TURE REMOVAL. 

(60) It is not desirable to dry lumber to a point much below jj 
that percentage of moisture which is natural to the climate in which U 



Irilll 



HI 

H 14 PRINCIPLES OF LUMBER DRYING 

II the lumber is to be worked up, and it is advisable to store the 

HI lumber in "dry storage" for several days after its removal from the 

H kiln, to enable it to adjust itself to its natural moisture content, before 

= it is worked up. 

S Types of Dry Kilns 

(61) In the preceding paragraphs have been described the gen- |j 
HI eral conditions and the factors necessary for the correct drying of 

§§ lumber in Dry Kilns. 

(62) While the various Dry Kiln systems in general present use 
H are known as: 

■ MOIST AIR KILNS, 
| CONDENSING KILNS, 
j| HOT BLAST KILNS, 

jj as a matter of fact any and all of the same must subject the lumber 

HI to the same conditions of preparatory Steaming, of H;eat, of Humidity |g 

|§§ and Air Circulation, and all must really work on the "MOIST AIR" 

H| principle if the drying shall be successful. 

(63) The only difference between the various (so-called) sys- 

jj terns consists in the means employed for the humidification of the kiln g 
§|| a£r, or in the means for moisture removal, or in the means for air jj| 
H circulation, but there can be "no marked difference" in the treat- 
Hi ment of the lumber from that herein set down as necessary for best 
H| results. 

jl (64) Of course, the adaptability, efficiency and economy of the IJ 

|j§ various designs of Dry Kilns will vary widely as does also their sim- 
§1 plicity of construction and ease and convenience of operation. 

(65) All of the present (so-called) systems, however, acknowl- g 
H edge two distinct types of Dry Kilns, each best suited to special con- | 
U ditions and requirements, the ' ' Progressive ' ' and the ' ' Compartment" g 

■ (or "Box") type. 



\m 



PRINCIPLES OF LUMBER DRYING 15 g 

Progressive Dry Kilns 

(66) The "PROGRESSIVE" TYPE of kiln differs from the 
"COMPARTMENT" or "BOX" kiln in that all the varying con- g 
dkions of treatment through which the lumber must pass in its drying 
process, are simultaneously and continually maintained in progressive j§§ 
order in the various adjoining portions of the kiln, and the lumber 
cars are gradually "progressed" through these conditions and ex- ^ 
posed to their action, the lumber entering the kiln "wet" on one end H 
and leaving the same "dry" on its opposite end. 

(67) Whenever large quantities of lumber are to be dried of 
one species, or of several species containing nearly equal quantities g 
of moisture and permitting the use of equal temperatures, and (the 
lumber being of equal thickness) of equal drying time, then the g 
"PROGRESSIVE TYPE" of Kiln is to be preferred. 

(68) For best results, kilns of the progressive type should never H 
be less than 100 feet long and preferably should be longer, up to g 
150 feet. 

Compartment Kilns 

(69) When, however, a large variety of miscellaneous species g 
and thicknesses of lumber must be dried and comparatively small 
quantities of each, then it is only with difficulty and most careful at- g 
tention that these miscellaneous species and thicknesses of lumber g 
may be properly passed through a progressive type of kiln with any- 
thing like satisfactory results, and for such miscellaneous lots of |jj 
lumber, requiring varying temperature and varying period of time 

in treatment, a number of smaller kilns of the "Compartment" type g 
will prove more desirable because more efficient and productive of 
better results. 

(70) While in the "Progressive" type of kiln all of the neces- 
sary varying conditions of temperature and humidity are produced 
and maintained simultaneously and continuously in progressive order 
and the lumber is gradually "progressed" through these conditions, g 
just the reverse takes place in a "Compartment" Kiln. 

(71) In the "COMPARTMENT," or "BOX," or "CHARGE" 
type of kiln, the lumber piles remain stationary, while the various 
required conditions of steaming, low temperature with high humidity, 



II 



m 16 PRINCIPLES OF LUMBER DRYING 



gradually changing to high, temperature with low humidity are suc- 
cessively accomplished in same degree over the entire kiln space. 

(72) It is therefore, possible in "Compartment" kilns to read- 
ily adjust the conditions and periods of drying to the several species 
and thicknesses of lumber therein contained. 

Selection of Dry Kilns 

(73) The selection of the proper type of kilns should conse- 
quently not be lightly determined upon, nor should the same be gov- 
erned entirely by consideration of space, but a careful estimate of 
the species and thicknesses of dry lumber as required annually and 
monthly should be prepared and submitted to the consideration of 
some party qualified to render competent advice. 

(74) Next in importance to the proper determination of the 
type of kiln, is the proper selection of the METHOD of PILING to |j 
be adopted. 

(75) The "maximum" as well as the "average" length of the 
lumber must be considered in this selection, and also the general lay- jj 
out of the plant and movement of the lumber. 

(76) Both the "CROSS-PILING" and the "END-PILING" 
methods have their advantages as well as their disadvantages. 

(77) Whenever the lumber is of uniform length and the con- 
ditions of its storage and movement through the kilns and to the HI 
workshop are otherwise favorable, then the "Cross-piling" method 
will be found very desirable. 

(78) If, however, the lumber is of varying lengths, becoming 
shorter from year to year (as hardwood lumber unfortunately seems 

to be destined to become) then the "Cross-piling" method is bound Jj 
to create not only a needless waste of Kiln space, but also unfavor- 
able and inefficient condition of air-circulation within the kiln. 

(79) Thus the proper method of piling also becomes a serious 
subject for competent consideration. 

(80) The important EXTERNAL FACTORS therefore, (aside J 
from the actual kiln construction and from the internal working con- Hf 



ADVICE TO OPERATORS 17 |§ 

dition of the kiln proper), on which depend not only successful and I| 
satisfactory drying, but also efficiency and economy of the entire 
operation are : 

l.-Proper selection of the TYPE of kiln. 

2.-Proper selection of the METHOD of PILING. 

3. -A carefully designed and installed STEAM SUPPLY 

SYSTEM. g 

4.— A carefully designed and installed CONDENSATION ( 
REMOVAL SYSTEM. 

5. — And last, but not least, a logical and systematic MOVE- 
MENT of the LUMBER from STORAGE THROUGH KILN to 
WORKSHOP, with well designed and well constructed KILN J 
CARS, TRANSFER CARS and other accessories. 

General Operating Instructions 

(81) These instructions contain in proper order only such ad- H 
vice and directions as apply with equal force and importance to any 
type of kiln manufactured by the A. H. ANDREWS CO., and the || 
same will be supplemented by separate bulletins containing concen- 
trated, detail instructions governing the correct operation of: 

"ANDREWS" MOIST AIR PROGRESSIVE KILNS, 
1 ' ANDREWS ' ' MOIST AIR COMPARTMENT KILNS, 
"ANDREWS" CONDENSING PROGRESSIVE KILNS, 
« ' ANDREWS ' ' CONDENSING COMPARTMENT KILNS. 

(82) These detail instructions in turn will be supplemented by j§| 
TABULATED SCHEDULES for the drying of the most important 
species of lumber and their several thicknesses and by proper forms 

of KILN RECORDS. 

(83) Assuming a complete Dry Kiln installation of correct de- g 
sign and construction, ready for operation, the operator's first at- 
tention must be directed to the 

Loading of the Cars 

(84) The wheels of the car bunks generally have double flanges = 
and should be always set upon the rails so that the corresponding j 



m 18 ADVICE TO OPERATORS 

Hi flanges (right or left) of all wheels shall be flush against the respective 

H rails. To prevent mistakes it is best to adopt a uniform rule to always 

HI place the same (side) flange of each wheel against the rail. This will 

j§ prevent binding and promote easy, travel of the lumber cars upon the 

Jf tracks. 

(85) For best and quick results in drying it is necessary to pay 
H particular attention to the PILING. A properly laid, straight and 
HI heavy FOUNDATION of planks or beams across the car bunks is ab- 
= solutely essential if straight lumber is desired. Position of these 
HI foundation planks or beams should be reversed with each fresh pile 
Hi of lumber placed thereon in order that same may be kept straight. 

(86) All sticks should be planed to parallel surface and should 
H be about y§ i^h to 1% inch thick by about iy 2 inch to 2 inches wide. 
§H Sticks must be placed directly over the wheel bearings of each set 
HI of bunks, and in between as reasonably close as possible (18 inches 
HI to 24 inches centers) in order to prevent any chance for warping. 
HI Sticks must also be placed at the two ends of each pile or as near 
§§ thereto as possible. The greater the height of the pile, the greater 
HJ should be the thickness of the sticks. It is not well to pile the lumber 
HJ higher than ten feet above tracks. 

(87) Each vertical row of sticks should be plumb, one above 
HJ the other. In the bottom layers of the lumber the vertical air- 
j§ spaces between the boards should aggregate not less than two-fifths 
HI of the entire surface of the respective layers and this air space may 
HI gradually decrease toward the top of the pile. The help performing 
HI this work must be impressed with its importance and with the fact 
HJ that lumber cannot be dried successfully if the air cannot freely dr- 
ill culate through the pile. One-half of the difficulties arising in dry 
§§ kilns can be directly traced to improper piling and sticking. 

(88) As far as possible the ends of each pile should be laid 
HI up straight and square at either side regardless of the length of the 
HJ lumber. This can be accomplished by intelligent alternating of short 

| and longer lengths, and of judicious use of extra sticking where neces- 
Hj sary. 

(89) It is important that all lumber be placed with the heart 



1 



Illlllllllllllll 
ADVICE TO OPERATORS 19 H 

side towards the bottom of the kiln. Correct piling of lumber will not 
necessarily cost any more in labor than slip-shod piling, and will 
yield a large return per annum for the exercise of a little extra care 
§jj and supervision. 

(90) Lumber of the same species and thickness only should be 11 
H§ piled upon the same car. 

(91) If this is not possible, then lumber of the same thick- 
ness, but of different species requiring same temperature, humidity 
conditions, and drying periods of equal length, may be combined in 

| the same carload, but lumber of different thickness should not be 
placed upon the same car, otherwise the drying period required for 
the lumber of greatest thickness must also govern the drying time of jjf 
HI the lumber of all lesser thicknesses. 

Placing of Lumber into Kiln 

(92) Properly designed kilns of the "PROGRESSIVE" type 
I are so proportioned that a number of cars of "wet" lumber may be 
| entered daily into same, equal to the number of carloads of "dry" 
\ lumber daily removed from the kiln, and so that ample space shall 
| remain for the daily progress of the required number of cars through 

I the various conditions of drying as per the schedule for the respec- fU 
U tive species and thicknesses. 

(93) A space free and clear, of at least six inches should always 
| be maintained between adjoining lumber piles. This is absolutely 
| necessary for proper circulation of the air around and through the 

I ends of the lumber piles. The same space requirement also holds J 
I good as to proximity of cars to doors or end walls, a little more space, 
\ if obtainable would be better. 

(94) In the case of ' ' COMPARTMENT " or " BOX ' ' kilns, the 
\ entire kiln track space may be filled with cars of "wet" lumber, pro- 

I vided that the necessary "free" space is maintained between cars jj| 
\ and between end-cars and walls or doors as set forth in preceding 
jl paragraph. 

(95) The steaming process of the lumber in either type of kiln 

iiiiiuiiiiiiiiiHiiiimiuiiiiiiiiiiiiiiiiiiiiiiiiifiiiiiiiiiiimiiiiimiiiiiiiiivmimiiin 



I 20 ADVICE TO OPERATORS g 

= is the same, and in either case is governed by the age, species and 
jl thickness of the lumber. 

(96) The steam spray must be turned on immediately after 
i= fresh lumber has been placed into the kiln, in order that the surround- 
= ing air may become ''saturated" with moisture as quickly as possible, 
HI and before the kiln temperature can communicate to the lumber. 

(97) In Box or Charge kilns the heating coils must be almost 
B "shut off" when fresh lumber is placed into the kiln and the "first 
B warming up" of the lumber shall be by the live steam of the spray, 
HI except that a small amount of steam may be passed through the 
B steam coils to prevent the condensation thereon of the moisture. If 
B this does not prove sufficient to bring the kiln temperature to the 
B desired degree, then more steam may be gradually admitted to the 
B heater coils, until the correct temperature has been reached. 

(98) In the case of "Compartment" or "Box" type kilns all 
Hi air supply and removal openings must be tightly closed during the 
B steaming process. This is important. 

H (99) The length of time during which the wood must be g 

B "steamed" preparatory to drying will depend upon the length of 

§| time which has passed since the lumber has been cut, upon the species g 

B of wood and the thickness of the lumber, and is set forth in detail 

jjl in the appended Drying Schedules. 

jl Actual Drying 

(100) After the steaming period, the lumber must be moved 
U forward, in the case of "Progressive" type kilns, into air of higher 

B temperature, less humidity and greater circulation as per proper |g 
§§ schedule for the species of thickness of the lumber being dried. 

(101) In the case of "Compartment" or "Box" kilns the 
B temperature and circulation are increased and humidity is reduced 
B as per respective schedule. 

(102) Correct progress of drying requires that from the time = 
Hj when steaming of the wood ends and actual drying begins the tern- j| 

■ 



§ 
ADVICE TO OPERATORS 21 j| 

perature of the kiln should be gradually increased as per schedule, |j 
until the greatest allowable maximum (for the species of wood in kiln) §§ 
has been reached, and that then the temperature shall be held sta- 
tionary at its maximum, while the humidity of the kiln air is gradu- 
ally reduced (strictly as per schedule and no faster) until at the 
close of the drying operation it shall have reached the lowest permis- §= 
sible minimum, scheduled for the species and thickness of the drying = 
wood. 

Interruptions to Drying 

(103) Whenever it becomes necessary from any cause and at | 
any time to materially reduce the temperature of the kiln air, then g 
the operator should immediately open up the steam spray in order to j 
maintain the correct amount of humidity until the lumber shall have fi 
cooled to the degree of the kiln air, otherwise the heat stored up in g 
the lumber would cause rapid surface drying and the troubles result- § 
ing therefrom. 

(104) If it is necessary (in the case of interruption of the ]| 
steam supply) to watch and maintain the humidity when the kiln U 
begins to cool off, it is doubly necessary to supply a sufficient amount [ 
of moisture when the interrupted steam supply is again resumed and 1| 
the lumber begins to heat up. 

(105) The extra moisture to be thus supplied should at least j 
correspond in amount with the moisture called for by the schedule jjj 
at the time of interruption of the steam supply (or the temporary g 
cooling of the kiln). It might be greater, but should never be less. 

(106) During any such interruption of the steam supply the ] 
circulation of the air within the kiln should be suspended as far as II 
possible and all openings and dampers carefully closed tight to pre- j 
vent loss of heat and principally loss of moisture. 

Measurement of Temperature and of Humidity 

(107) In order that a dry kiln operator may properly conduct g 
and control the drying operation of the lumber within the kiln it is j 
absolutely necessary that he should be able to ascertain at any time I 



H 22 ADVICE TO OPERATORS 

11 the correct temperature, and humidity of the kiln without unusual 

Hi effort and without disturbing this temperature and humidity by the 

H opening of large doors. 

(108) For the purpose of ascertaining the kiln temperature 

HI and at the same time the humidity, the most suitable and accurate 

= instrument is a " maximum registering" HYGROMETER. 

Hi (109) The Hygrometer consists of two high grade, sensitive 

HI thermometers mounted upon a heat, moisture and acid proof casing. 

§j Each thermometer is equipped with a simple device which registers 

H the highest point reached by the mercury and which may readily 

§j be re-set for the next reading. The bulb of one of these thermometers 

Hi is exposed to the free air, while the bulb of the other thermometer 

j§ is covered by a silk mantle, the lower end of which is inserted in a 

HI suitable water reservoir, and this bulb is thus kept covered with 

H a film of moisture by capillary attraction of the water from the reser- 

m voir. 

]| (HO) As then the moisture evaporates from this bulb, the 

§| heat of vaporization (latent heat) is abstracted from the bulb and 

Hf the thermometer indicates a "depression of temperature" below that 

gj shown by the adjoining "dry" thermometer which is in proportion 

gj to the rapidity of evaporation of the moisture from its "wet" bulb. 

jj This rapidity of evaporation in turn being dependent upon the 

!§ amount of moisture content of the surrounding air and its consequent 

H ability to absorb additional moisture, the "temperature difference" 

j§ of the two thermometers becomes a positive indicator of the humidity 

U condition of the air. 

(111) A form of hygrometer, called hygrodeik, equipped with 
Hf a chart and indicator arrangement for the calculation of the humidity 

"percentages" is frequently supplied by the dry kiln builders, but 

II since it has no "registering" feature it must be read quickly, and 

jj owing to this fact cannot be placed very far from the doors into the 

Hj kiln. It is not as desirable as the previously described form of "maxi- 

H mum registering" Hygrometer. 

(112) Moreover the computation of the relative percentage of 
|j humidity is wholly unnecessary and time wasting. If the kiln oper- 



m 



ADVICE TO PERATORS 23 M 

ator is supplied with a correct schedule of simultaneous "dry" and | 
"wet" bulb temperatures which he must obtain and maintain in the 
kiln during the various stages of the drying period, then he is no 
longer concerned with the relative percentage of the moisture. He 
knows that the moisture is there if his dry and wet bulb thermometers 
read as scheduled, and he knows how to make adjustments, if they do 
not read so, without extra computation of percentages. 

(113) Careful provision, of course, should be made in the con- 
struction of the kiln for the insertion of a "dry and wet bulb" 
Hygrometer, at such points of the kiln as will bring the instrument 
well within the air currents of the kiln and will enable reasonably 
correct "average" readings. 

(114) Whenever possible the Hygrometer should be projected 
(by a suitable means) into the kiln, a reasonable distance from all 
openings (especially doors) until the operator has learned by experi- 
ence, to judge and allow for, the influence of such openings and doors 
upon the correctness of the temperatures indicated by the Hy- 
grometer. 

(115) It my not be amiss to caution here that the correct- 
ness of the indications of a Hygrometer of any form or make, de- 
pend strictly upon the ability of the wick of the wet bulb to keep 
this bulb "wet." The use of pure distilled water and freedom 
from dirt (and particularly grease) will prolong the life of the 
wick and increase the correctness of the readings. These wicks are not 
expensive, should always be kept on hand and changed as soon as 
they show any signs of hardening. 

(116) The correct "dry" and "wet" bulb temperatures are 
stated in the "ANDREWS" schedules for any point in the drying 
period of the various species of wood, considering age and thickness. ||| 
These schedules are supplied only to the purchasers and users of 
Dry Kilns designed and constructed by "THE A. H. ANDREWS 
CO." 

(117) By way of illustration of the great influence which the 
humidity of the surrounding air exercises upon the drying of the |j 
lumber in a kiln, attention is directed to the following facts : 



m 24 ADVICE TO OPERATORS 

(118) On a bright summer day (good drying weather) with 

=J temperature of the air at 85 deg. F. and the humidity at 50 per cent, 

H each cubic foot of air would sustain 6.36 grains of moisture. 

HJ (119) To reach the point of "Complete Saturation" (100 per 

Hi cent humidity) this summer air would have to absorb additional 

HI moisture to the same amount, when it would contain a total of 12.7 

II grains of moisture. 

II (120) The maximum capacity for "absorbing moisture," which 

HJ means for "drying," of such a summer day, would be equal to 6.36 

HI grains of moisture per each cubic foot of air. 

Hf (121) Comparing this with dry kiln conditions we find that 

H if the temperature in the kiln were 130 deg. F., and the humidity; 

HJ likewise 50 per cent, then each cubic foot of kiln air would support 

Hf 22.5 grains of moisture and would be capable of absorbing an ad- 

H ditional amount of 22.5 grains before it reached its saturation point. 

U (122) The DRYING CAPACITY of this Kiln Air, therefore, 

§§ would be more than three times as great as that of the stated summer 

H day. 9HI 

j| (123) If, on the other hand, the temperature of the Dry Kiln 

HI Air remained at 130 deg. F., and the humidity were reduced from 

HJ 50 per cent to 30 per cent, then the moisture contents per cubic foot 

HI would be but 14 grains, and its capacity for additional moisture to 

§1 saturation point would be 31 grains. 

HJ (125) The "drying" capacity of this kiln air, therefore, would 

HJ be nearly five times as great as that of a good "drying" summer 

B day. 

(126) If we consider the above stated facts in connection with 

H the drying of lumber, we are at once impressed with the necessity 

HJ that "since lumber must be dried slowly," the air must be so con- 

= ditioned that it shall not be able to absorb moisture any faster than 

HI same can be taken from the lumber without injury to the wood, and 

HJ the only way by which this can be accomplished is to increase and 

Hi maintain by suitable means, the moisture content of the air sufiiciently 

Hi high to reduce its drying capacity to the desired point. 



|iiiiiiiiiiiiiiiiiiiiii!iraiiiiiiiiiiiiiiiiiiiiiiiiii 

ADVICE TO OPERATORS 25 

Final Degree of Dryness 

(127) It depends upon the uses for which the kiln dried wood 
is intended as to whether the same shall be dried to the point of lowest H 
possible moisture content (bone dry) and of greatest shrinkage, or 
H if the drying process is to be terminated when the wood has at- 
H tained that degree of dryness at which the wood will remain in use, 
g and which degree is controlled by the average temperature and 
: I humidity conditions of the atmosphere permanently surrounding the 
lH wood in its final use. 

m (128) Whenever a minimum amount of "swelling" and i§ 

H "shrinkage" in the manufactured stock is of prime consideration, H 

|§ then drying to minimum possible moisture content is advisable, pro- jj 

H vided, that the wood is given sufficient time after cooling, to re-absorb jj 

|§ under natural conditions (protected from the influence of the |§ 

m weather) that amount of moisture which its reduced hygroscopicity gj 

H will require. H 

(129) Wood which has been thus dried to bone dry condition |j 

H§ will not again absorb as much moisture from the atmosphere as wood §j§ 

jj which has been dried to a lesser degree. 1 1 

HI (130) The time required for the re-absorption of the "natural" ji 

1 4 moisture content of the kiln-dried wood will vary with the species and H 

thickness, but for 4/4 stock from five to ten days will generally be j| 
HI sufficient for this "acclimatization." 

(131) If, on the other hand, strength of the wood is of first jj 
consideration, then the drying should be terminated when the mois- 

jj ture content of the wood has reached 5 per cent to 6 per cent, and |§j 
the wood should then be removed from the kiln and allowed to cool. 

(132) In either case it is desirable to allow a period of rest J| 
(under shelter and in reasonably warm and dry atmosphere) be- |j| 

g fore the wood is manufactured. H 

Testing for Moisture Content 

(133) Of equal importance to the dry kiln operator with the M 
knowledge of the temperature and humidity conditions of the kiln = 



m 26 ADVICE TO OPERATORS 

= throughout the entire drying process, is the knowledge of the "MOIS- 
J TURE CONTENT" of the wood before, during and at the end of the 
jjj drying period. 

HI (134) It is only by means of his knowledge of the initial mois- 
§j ture content that the dry kiln operator can select the proper drying 
HI schedule for the stock about to enter the kiln. The moisture content 
Hi ascertained during the drying period enables him to judge the prog- 
Ill ress of moisture elimination, and to determine the necessary length 
§§ of the drying period. 

(135) Tests made near the end of the drying period will not 
= only prevent the " under-drying" or "over-drying" of the wood, but 
(§ will also teach the operator to correctly judge condition and appear- 
U ance of the lumber at various degrees of dryness. 

JH (136) These tests should be twofold, and if same are to be of 

Hj value, must be made with care and accuracy. One test is by the 
■ measurement of the "SHRINKAGE," and the other by "LOSS OP 
jj WEIGHT." 

(137) The procedure in the making of these tests is as follows: 

(138) First — Prom each carload of lumber to be dried, select 
HI a board which represents (as nearly as can be determined by mere 
HI inspection) the wettest portion of the stock. 

(139) Second — From the central portion of this board cut a 
U piece approximately 20 inches long, and parallel surface the edges 
!H of this test piece. 

(140) Third — From this test piece after surfacing of its edges 
(H out a three inch strip across grain, and from this three inch strip 
Hi cut a three-eighths inch disc likewise across grain. 

(141) Fourth — Mark each of the three test pieces with the 
HI number of the kiln, number of the kiln car, the date and the number 
11 of the test piece. 

(142) Fifth — Enter these data into the dry kiln record. 

(143) Sixth — Place the large (20 inch) test piece upon its re- 
JH spective car in such position that it shall receive "average" treatment 
= in the kiln and shall at the same time be accessible for further test cuts. 



ill 



ADVICE TO OPERATORS 27 

(144) Seventh — Put away the three inch test piece in such a g 
location and manner that it shall not lose moisture, nor absorb any. fjj] 
This piece may be required to check original moisture content. 

(145) Eighth — Carefuly measure from edge to edge (across 
grain) the thin (three-eighths inch) test disc and determine its exact 
green cross grain dimension. Then carefully weigh the same piece on 
sensitive (metric) scales and determine its correct green weight (in 
grammes). ||| 

(146) Ninth — Next enter this dimension and weight into the 
D. K. Record. 

(147) Tenth — Place this thin test disc upon a hot and dry jj 
surface (steam pipe, boiler top or engine clyinder) and dry same 

to minimum moisture content (bone dry). 

(148) Eleventh — When bone dry, measure again the length [J 
of this disc (across grain) and figure percentage of shrinkage, and 
mark both thereon. 

(149) Twelfth — Enter into Dry Kiln Record the dry dimension jjj 
and weight of this test strip. 

(150) Thirteenth — After steaming of the lumber another test 
strip three-eighths inch thick should be cut from the large (20 inch) 
test piece in the kiln, and this should again be carefully measured and 
weighed, the measurements and weights and percentages of loss of 
each of same be marked thereon and also entered into the Dry Kiln 
Record. 

(151) Fourteenth — Several such tests should be made at regular Hi 
intervals during the drying period and carefully registered in the 
Dry Kiln Record. A careful comparison and study of the shrinkage 
and weight loss throughout the drying period will in a brief time 
develop expert judgment on the part of the dry kiln operator and 
enable him to readily determine the progress of drying, as well as the 
minimum of time required for best results with different initial mois- 
ture content of the lumber. 

(152) Ordinarily near the end of the drying operation when the 
amount of shrinkage between the measurement of the strip cut from 



iililllllllllllllllHIIIIIIIIIIlllll iiiiiiiiiiiiiiiiiiiiiiiiiiiin 



jj 28 ADVICE TO OPERATORS 

HI the test piece in the kiln and its "bone dry" measurement shows 
close to 1 per cent, and when the difference in weight of the same 

HI strip (from the Mln and after bone drying) shows a moisture content 

§§ of not more than 5 per cent on the final test, the lumber on the re- 

H spective car may be considered as sufficiently "dry" for all practical 

= purposes in ordinary manufacturing. 

(153) For the best interests of "economy" and "efficiency" in 

Jj the drying and in the manufacturing of the lumber, however, it is 

JH desirable that test pieces be taken from "factory dry stock" during 

JH the various stages of manufacture, and the same be laid aside (near 

§fj the location of the respective operations from which they were se- 

§ cured) for a period of at least 10 days, so that the same shall become 

H adjusted to the moisture condition of the surrounding atmosphere, 

H after which time suitable test discs shall be cut and dried "bone dry" 

§§ and their shrinkage and moisture content determined in the usual 

H manner. 

|il (154) The average moisture content so ascertained will then 

fU represent the correct "final moisture content" which the lumber 

PI should have when it leaves the Mln for the shop. 

H (155) To find the percentage of shrinkage, subtract the "bone 

= dry" dimension of the test disc from that which it had before bone 

fU drying, and divide this difference by its bone dry. dimension. Then 

H multiply the quotient by 100, and the result will express the amount 

fU of shrinkage in per cent of the "bone dry" dimension. 

(156) To find the percentage of moisture content, subtract the 
Ji "bone dry" weight of the test disc from that which it had before 
§§ bone drying, and divide the difference by its "bone dry" weight. 
H Then multiply the quotient by 100, and the result will express the 
iH amount of moisture contained in the sample (before bone drying) 
H in per cent of its "bone dry" weight. 

Dry Kiln Records 

(157) System is essential to Progress and Success in every 
jj undertaking. Whenever success is dependent upon the faithful at- 
Hl tention to a number of small but important details, then a proper 



m 



ADVICE TO OPERATORS 29 

system for the control and supervision of these details becomes very 
necessary, especially when the results of oversight or carelessness 
may involve considerable money loss, not only in raw material (dry 
lumber) but also sometimes in manufactured stock. 

(158) System requires the keeping of records, and probably in 
no branch of the wood working craft will the keeping of complete 
and correct records pay so large a return, as in the kiln drying of 
the lumber. 

(159) The pages of this Bulletin, we sincerely hope, may prove 
of value to many in pointing the way to success in the drying of 
lumber, but in the end the same can only "point the way" and ex- 
plain the actual process of moisture elimination and the resulting 
changes in the wood structure as far as the same have been ascer- 
tained. 

(160) It will depend upon the individual operators of dry kilns 
to "TEST OUT FOR THEMSELVES" the CORRECTNESS of 
the precepts herein set down and the application of the stated prin- 
ciples of drying to their particular material, conditions and sur- 
roundings. 

(161) EXPERIENCE must, therefore, remain the supreme 
teacher, intelligently assisted by such advice as is based on scientific 
fact. 

(162) The results of actual experience, carefully recorded, com- 
pared and studied, lead to a superior knowledge and control of the 
subject, and if practically applied, lead to superior results. There- 
fore, it is to the interest of every industry which requires properly 
kiln dried lumber to keep records as complete as possible along the 
lines herein set down. 

(163) Dry Kiln Records should contain a concise, though brief 
synopsis of every car of lumber passing through the kiln, and should 
show the conditions successively surrounding this car from beginning 
to end of the drying period, as well as the successive condition of 
the lumber itself. 

(164) The amount of time and labor expended in the proper 
keeping of these records is not large, but the satisfaction, education 



if 



fli!!!l!ll!li!i!!!l!lllllllllllll[llillilll!l!llll 

H 30 ADVICE TO OPERATORS 

§§ and direct economic profit derived therefrom will be found of con- 
|H siderable permanent value. 

(165) The Engineering Service Department of THE A. H. 
H ANDREWS CO. is preparing suitable Record Books for the use of 
§§§ the owners of the dry kilns of the several types of "ANDREWS" de- 
m sign and these will be supplied at a nominal cost. 

jj Instruments 

Jj (166) The most important of all instruments and absolutely 

j§ necessary is the HYGROMETER for the measurement of tempera- 

m tures and humidities. Without the proper use of a reliable Hygrom- 

jj eter, correct dry kiln operation is unthinkable and becomes guess 

m work. 

(167) Next in importance comes a suitable, correct GAUGE for 
II measurement of shrinkage, and a suitable, correct SCALE for deter- 
Hl mination of moisture content, of the test strips. Both of these are 
§j also necessary to the proper operation of the kiln, and are fur- 
H nished in superior quality and at moderate cost by THE A. H. 
U ANDREWS CO. 

(168) WATER THERMOMETERS are indispensable to the 
jj proper operation of "CONDENSING TYPE" Dry Kilns. These 
|H should be correct, and so located that the same may be easily read 
jj from the outside of the kiln. 

j§ (169) The Engineering Service Department will advise owners 

K and operators of "ANDREWS" Condensing Kilns as to the proper 

jj selection and location of the Water Thermometers in line with recent 

jj improved practice. 

(170) RECORDING THERMOMETERS, giving a continuous 

B record of the DRY KILN TEMPERATURE, over a 24-hour, or a 

= 168-hour period, are very desirable, and whenever possible should 

jj be installed upon each kiln, but their extensions must be of such g 

HI length that the "bulb" of the thermometer will be located at that 

jl point of the kiln where it will register correctly the "average" tern- jj 

jj perature conditions, while the recording works of the instrument jj| 

JH must remain outside of the kiln. 

H 



ADVICETOOPERATORS 31 

(171) The correct installation of Recording Thermometers re- 
quires certain engineering knowledge and information which is at 

| the disposal, free of cost, of the purchaser of these instruments from 
THE A. H. ANDREWS CO. 

(172) RECORDING STEAM PRESSURE GAUGES are of 
great importance in some plants while the same would be perfectly 
useless in others. Correct advice will be cheerfully furnished free 

! of cost, by application to the Engineering Service Department of THE 
| A. H. ANDREWS CO. 

Care of the Instruments 

(173) It is probably needless to state that all delicate and fragile 
j instruments require considerate and careful treatment if the same are 

H to prove reliable in their indications. 

(174) Particular attention must be paid to the wick or capillary J| 
: tube of the "Wet Bulb" thermometer of the Hygrometer. These 

j silk or cotton tubes will harden and must be renewed frequently if 
jj| reliable readings are to result. 

(175) The water used in the wells of these instruments should 

I be filtered, pure distilled water and nothing else. If condensed steam jjj 
! is used, then it must be filtered through several layers of filter paper 
= to exclude any foreign substance and particularly "grease." 

Care of Dry Kilns and Equipment 

(176) A few words pertaining to the proper care of dry kiln jj 
H| buildings and equipment will not prove amiss. 

(177) Continued high temperatures and humidities are destruc- 
| tive to nearly all of the materials used in the construction of dry 
\ kilns. It therefore becomes necessary to protect as far as possible 
f these materials by means of coating or impregnating the same with 
I heat and moisture resisting and fire-proof preservatives. Brick and 
1 concrete walls must be made and maintained moisture proof, while 

§ structural steel must be treated against rust, and as far as possible 
1 must be covered with materials impervious to moisture, and wood 



I 

| 32 ADVICE TO OPERATORS | 

j§ construction and canvas doors must be made and maintained fire- 
= proof and proof against moisture and rot. 

(178) The water coils of condensing dry kilns will require 
j= occasional surface cleaning from the crust of rust forming thereon 
HI and less frequent removal of inner scale and mud deposits (depend- 
g ent upon the quality of the cooling water). In recent construction 
HI the condenser coils and all water connections are made of galvanized 
H materials. 

(179) It must be remembered that a single drop of oil (if 
U put in the right place) will often work wonders in the movement of 
= things which run on wheels. Car bunks and transfer cars should, 
j§ therefore, receive at regular and frequent intervals their proper 
HI quota of ' ' drops " of oil and in the ' ' right place. ' ' The oil best suited 
HI to the conditions to which the dry kiln car bunks are exposed is a 

H good quality of cylinder oil, into which has been mixed a liberal j§ 

jj quantity of best grade of Dixon's Flake Graphite. The same lubri- 

= cants will also work well on the bearings of transfer cars, but in 

= each case must be warmed before application. 

(180) The steam trap has not as yet been built which requires g 
HI no further attention, once the same has been installed, and there- 

I| fore the condensation removal from the heater coils of the dry kilns g 

HI will always prove an interesting and profitable field for inspection 

g and maintenance, especially where a trap system is employed which g 

jj returns condensation directly to the boilers. 

(181) "What to do" in each and every case, would fill a bul- = 
g letin more voluminous than this, and then perhaps would not cover jj 
Hi the particular information desired by the friends of the "AN- 

jjj DREWS" Drier Equipment. Requests for information are there- jj 

g fore invited and will be cheerfully answered, free of cost, and cor- =j 

g rect information will be supplied whenever the same may benefit g 

g the owners and operators of "ANDREWS" Dry Kilns. 

Additional Detail Information 

(182) Purchasers, owners and operators of any of the several 

S types of dry kilns designed and sold by THE A. H. ANDREWS CO. |j 

III 



ADVICE TO OPERATORS 33 

will, upon application, be supplied with additional DETAIL OPER- jj| 
ATING INSTRUCTIONS and with DRYING SCHEDULES. 

(183) In conclusion is repeated the invitation to "PROSPEC- 
TIVE PURCHASERS of DRY KILN EQUIPMENT" to make free 

use of the Engineering Service Department of THE A. H. AN- g 
DREWS CO. and its exceptional facilities, information and experi- 
ence, for the proper determination of their particular requirements, HI 
and for the selection of the types of kilns best suited to these re- 
quirements, and finally for the proper, efficient and economic progress jj 
of the lumber from the receiving track through green storage, dry 
kilns and dry storage to the shop. 

(184) In return for such services the prospective purchaser of g 
dry kilns is under no obligation whatever, unless it be to give fair §g 
consideration to the expert advice submitted, which consideration 
will at once disclose the superior care and detail attention given to g 
his problem, and the correctness of the advice and information sub- 
mitted, and such consideration will also prove convincingly the fact |l| 
of the SUPERIORITY in DESIGN and MATERIAL of the Dry Kiln 
Equipment supplied by THE A. H. ANDREWS CO. 



till 



INDEX 

Paragraphs Pages ^= 

Actual Drying 100-102 20-21 H 

Additional Detail Information 182-184 32-33 

Air Circulation 33-42 9-10 

Air Circulation, in Condensing Kiln 57- 58 13 

Air Circulation, in Moist Air Kiln 55- 56 12 j}§ 

Air Dried Lumber, Case-hardening of 12 5 

Air Movement 33-42 9-10 

Air Movement, in Condensing Kiln 57- 58 13 

Air Movement, in Moist Air Kiln 55- 56 12 j|i 

Back Pressure Valve 47 11 ^ 

Care of Dry Kilns and Equipment 176-181 31-32 Jf 

Care of Instruments 173-175 31 j|l 

Circulation of Air 33-42 9-10 =j 

Circulation of Air, in Condensing Kiln 57- 58 13 

Circulation of Air, in Moist Air Kiln 55- 56 12 

Cleaning of Condenser Coils 178 32 ||| 

Compartment Kilns 69- 72 15-16 §j| 

Condensation Removal, Importance of 48- 49 11 §g 

Controlling Factors of Drying 43- 44 10 == 

Correct Drying Conditions 4 HI 

Detail Operating Instructions 182 32-33 j 

Drying Factors 43- 44 10 H 

Drying Heat 45-49 10-11 h 

Drying Interruptions 28- 32 8 j 

103-106 21 (J 

Drying Schedules 182 32-33 | 

Drying, Speed of 26a- 27 7- 8 HI 

Dry Kiln Records 157-165 28-30 j§ 

Dry Kiln Temperature 45- 49 10-11 =§ 

Engineering Service Department, Purpose of 5-7 3- 4 = 

Exhaust Steam, Economy of 47 11 = 

Exhaust Steam, Increased Coil Surface Required .... 47 H H 

Factors Controlling the Drying 43- 44 in HI 

Final Degree of Dryness 127-132 25 3 

First Principle of Drying 15 5 = 

General Operating Instructions 17 = 



INDEX — Continued 

Paragraphs Pages s= 

Heat 45-49 10-11 

Heating of Lumber 18- 19 5 == 

Humidity 50-54 11-12 |j 

Humidity and Temperature, Measurement of 107-126 21-24 

Hygrometer 108-110 22 g 

Instruments 166-172 30-31 U 

Interrupted Drying 28-32 8 

103-106 21 |j 

Loading of Cars 84-91 17-19 g 

Measurement of Temperature and Humidity 107-126 21-24 ^ 

Moisture Content, Testing for 133-156 25-28 g 

Movement of Moisture 21- 24 6-7 = 

Oiling of Car Bunks and Transfer Cars 179 32 j| 

Placing of Lumber in Kiln 92-99 19-20 g 

Preface 3 HI 

Pressure Reducing Valve 47 11 = 

Progressive Dry Kilns 66- 68 15 = 

Record Books 165 30 |j| 

Second Principle of Drying 20 6 = 

Selection of Dry Kilns 73-80 16-17 jj 

Speed of Drying 26a- 27 7- 8 g 

Steaming of Lumber 16 5 = 

Temperature and Humidity, Measurement of 107-126 21-24 

Testing for Moisture Content 133-156 25-28 

Third Principle of Drying 26 7 g 

Time of Drying 59-60 13-14 g 

Types of Dry Kilns 61-65 14 g 



Progressive or Charge Type 

| Condensing 
| Lumber Driers 

j§ Designed and Constructed by 

| The A. H. Andrews Go. 

■ Chicago 

Are Selected by Those Who Know 

M BECAUSE: 

jj Their Temperature Regulation is perfect and convenient. 

H Their Humidity Control is practical and easy to 
H accomplish. 

B Their Circulation is positive in action and large in 
jj volume. 

jg Their Drying Time is reduced to practical minimum, 
owing to constant and correct conditions of 
Temperature, Humidity and Circulation. 

M Their Results are ahead of all other Dry Kilns. 



"ANDREWS" 

Moist Air Kilns 

Are Superior to Any of their Type 

Temperature, Humidity, Circulation 
Are Easy to Obtain and to Control 



Progressive or Box Type 



Designed and Constructed by 

The A. H. Andrews Co, 

CHICAGO 



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"ANDREWS" 

Canvas Doors 



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Are Used on Largest Dry Kilns in This 
and Foreign Countries 



Double Curtains are 
Efficient Heat Savers, 
easily and quickly at- 
tacked ana operated 
and are long lived. 



MADE IN ALL SIZES BY 

The A. H. Andrews Co. 

CHICAGO 



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All Steel" Kiln Cars 

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Rails, Road or Shop Floor 



All Dimensions and Capacities 



Supplitd by 

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Chicago 



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Are different. 
Are smooth running. 
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Are cheaper in the long run. 

—Than Any Otljer Make 



Supplied in all Sizes by 

The A. H. Andrews Go. 

CHICAGO 



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"ANDREWS" 

Transfer Cars 

Cross or End Piling 



Are of better, 
heavier design, 
stronger con- 
struction, more 
effectively cross- 
braced, and run 
easier than any 
other good Trans 
fer Car offered. 

See Drawings on Pages 
44, 46 and 47. 

For details and prices — 
Address DRIER DEPARTMENT 

The A. H. Andrews Co. 

CHICAGO 



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"Andrews 

Positive 

Varnish Driers 



Positive forced Circulation oi purified fresh air. 
Positive and Automatic Control oi Temperature. 
Positive and Automatic Control of Humidity. 
Positive Improvement in Finish Hardness. 
Positive Reduction in Drying Time. 



Special Engineering Investigation and Design in each case. 



Supplied by 

Tke A. H. Andrews Co. 

CHICAGO 



LIBRARY OF CONGRESS 



017 111 499 8 



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